1. Field of the Invention
The present invention relates to a method for removing strain from a press-formed workpiece and to a forming press capable of carrying out the method.
2. Description of the Related Art
In many cases, strain remains in a press-formed workpiece or in a product obtained through finishing of the workpiece. Therefore, strain must be removed from the press-formed workpiece. Particularly, when a thin metal plate is subjected to press forming, removal of strain is very important. A product obtained through press forming of a thin metal plate (not greater than 0.5 mm in thickness) is, for example, a separator for use in a fuel cell (as well as an article disclosed in Japanese Patent Application Laid-Open (kokai) No. 2001-259752).
As shown in the enlarged schematic view of FIG. 13, a separator 1 for use in a fuel cell has many projections and recesses 1 a formed at its central portion. The separators 1 and electrolyte membranes 2 are arranged such that each electrolyte membrane 2 is sandwiched between the separators 1 to thereby form reaction chambers 3, into which hydrogen is introduced, and reaction chambers 4, into which oxygen is introduced, while the separators 1 are directly joined back-to-back to thereby form cooling chambers 5, into which cooling water is introduced. In order to achieve good joining of the two separators 1 and of the separator 1 and the electrolyte membrane 2, press-formed workpieces which are finished into the separators 1 must be free of strain. Also, other products obtained through press forming must be free of strain, and the same applied to press-formed workpieces which are finished into the products.